EP 0 713 689 A1 discloses a prosthetic knee joint with an upper part, and with a lower part fastened to the latter in an articulated manner. The coupling of upper part and lower part is effected via a multi-element, kinematic joint chain with at least four joint members, in which the members respectively connected to one another have a common rotation axis. The rotation axes extend substantially parallel to one another; in the starting position of the multi-element joint system, one joint member can execute two movements with respect to the other members connected to it, wherein at least one movement, following its initiation, blocks the other possible movement at least for the most part. With such a device, it is possible to permit a stance phase flexion without completely blocking a buckling of the prosthetic knee joint.
The problems of prosthetic knee joints with length-adjustable joint members are the relatively complex construction and the possibility that a geometric barrier of the joint system arises when giving-way during the stance phase flexion. A geometric barrier of a prosthetic knee joint is described, for example, in U.S. Pat. No. 5,314,498, in which the aim is to simulate the function of a natural knee joint by means of a polycentric construction and to permit automatic geometric locking in a simple manner.